U.S. patent application number 12/550159 was filed with the patent office on 2010-04-01 for production method for magnetic recording media and magnetic recording and reproducing apparatus.
This patent application is currently assigned to SHOWA DENKO K.K.. Invention is credited to Masato FUKUSHIMA.
Application Number | 20100079901 12/550159 |
Document ID | / |
Family ID | 42057214 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100079901 |
Kind Code |
A1 |
FUKUSHIMA; Masato |
April 1, 2010 |
PRODUCTION METHOD FOR MAGNETIC RECORDING MEDIA AND MAGNETIC
RECORDING AND REPRODUCING APPARATUS
Abstract
A production method for a magnetic recording medium on which a
stable lubricant layer can be formed even if unevenness remains on
the surface, and the thickness of the lubricant layer is not
reduced over time is provided. The method includes forming a
lubricant layer (12) on a surface of a magnetic recording medium
(30) by the steps of: applying, onto the surface of the magnetic
recording medium (30), a first lubricant (12a) with high
wettability of the surface of the magnetic recording medium (30)
with respect to the lubricant; and applying a second lubricant
(12b) onto the surface of the magnetic recording medium (30) onto
which the first lubricant (12a) has been applied.
Inventors: |
FUKUSHIMA; Masato;
(Chiba-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SHOWA DENKO K.K.
Tokyo
JP
|
Family ID: |
42057214 |
Appl. No.: |
12/550159 |
Filed: |
August 28, 2009 |
Current U.S.
Class: |
360/75 ; 427/127;
G9B/21.003 |
Current CPC
Class: |
G11B 5/855 20130101;
G11B 5/746 20130101; G11B 5/743 20130101; G11B 5/8408 20130101;
G11B 5/82 20130101; B82Y 10/00 20130101 |
Class at
Publication: |
360/75 ; 427/127;
G9B/21.003 |
International
Class: |
G11B 21/02 20060101
G11B021/02; G11B 5/84 20060101 G11B005/84 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 1, 2008 |
JP |
2008-223725 |
Claims
1. A production method for a magnetic recording medium, the
magnetic recording medium comprised a non-magnetic substrate; a
magnetic layer; and, on at least one surface of the non-magnetic
substrate, a magnetic pattern formed by magnetically isolating the
magnetic layer when seen from a side of a surface of the magnetic
recording medium, and the magnetic pattern being formed by the
magnetic layer and an isolated area defined around the magnetic
layer, and the isolated area having a recessed area with respect to
the magnetic pattern, wherein the production method comprises
forming a lubricant layer on a surface of the magnetic recording
medium by the steps of: applying, onto the surface of the magnetic
recording medium, a first lubricant with high wettability of the
surface of the magnetic recording medium with respect to the
lubricant applied to the surface of the magnetic recording medium;
and applying a second lubricant onto the surface of the magnetic
recording medium onto which the first lubricant has been
applied.
2. The production method for a magnetic recording medium according
to claim 1, wherein a molecular weight of the first lubricant is
smaller than that of the second lubricant.
3. The production method for a magnetic recording medium according
to claim 1, wherein after the first lubricant is applied to the
surface of the magnetic recording medium, the first lubricant
applied to the surface of the magnetic recording medium is
partially washed out and then the second lubricant is applied to
the surface of the magnetic recording medium.
4. The production method for a magnetic recording medium according
to claim 1, wherein the surface of the magnetic recording medium is
washed with water before the first lubricant is applied to the
surface of the magnetic recording medium.
5. A magnetic recording and reproducing apparatus comprising in
combination: a magnetic recording medium produced by the production
method for a magnetic recording medium according to claim 1; a
driving section which drives the magnetic recording medium toward a
recording direction; a magnetic head which includes a recording
section and a reproducing section; a device for causing the
magnetic head to relatively move with respect to the magnetic
recording medium; and a recording and reproducing signal processing
device which inputs signals to the magnetic head and reproduces
output signals from the magnetic head.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority of Japanese Patent
Application No. 2008-223725 filed Sep. 1, 2008, the content of
which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a production method for a
magnetic recording medium used for a hard disk device and to a
magnetic recording and reproducing apparatus.
[0004] 2. Description of the Related Art
[0005] Recently, applicability of magnetic recording devices, such
as magnetic disk devices, flexible disk devices and magnetic tape
devices, has increased significantly and their importance has also
increased. Recording density of these magnetic recording media used
for these devices has been increased significantly. With the advent
of technologies regarding a magnetoresistive head and partial
response maximum likelihood (PRML), surface recording density has
improved still more significantly. In recent years, recording heads
including GMR heads and TMR heads have also been introduced, which
has further increased the surface recording density by about
twofold a year. Regarding these magnetic recording media, there is
a demand further increasing the recording density in the future. It
is therefore necessary to increase coercive force, signal-to-noise
ratio (SNR) and resolution of the magnetic layer. In recent years,
efforts to increase the surface recording density have been made by
increasing track density simultaneously with increasing linear
recording density.
[0006] The most recent magnetic recording media have track density
of as high as 110 kTPI. As the track density increases, however,
magnetic recording information between adjacent tracks begins
interfering with each other. As a result, a magnetizing transition
area of a border area becomes a noise source, which may easily
decrease the SNR. The decrease in the SNR may directly lead to a
decrease in a bit error rate and prevent an improvement in
recording density.
[0007] In order to increase the surface recording density, it is
necessary to make the size of each recording bit on the magnetic
recording medium finer and to secure the biggest possible
saturation magnetization and the magnetic film thickness to each
recording bit. However, as the recording bit becomes finer, the
magnetizing minimum volume per 1 bit becomes small and recorded
data may disappear by flux reversal caused by heat fluctuation.
[0008] Since the adjacent tracks come close to each other, a very
highly precise track servo technique is necessary for the magnetic
recording device. Usually, information is recorded on a wide track
and reproduced in a narrower track in order to reduce influence
from adjacent tracks to the minimum. Although influence between the
tracks can be suppressed to the minimum by this method, it is
difficult to obtain a sufficient reproduction output and it is thus
difficult to provide a sufficient SNR.
[0009] In order to address the problems of the heat fluctuation and
reliablity of the SNR or to provide sufficient outputs, unevenness
along the track is formed on the surface of the recording medium so
as to isolate the recording tracks physically or magnetically from
one another to increase the track density. Such a technique will be
called herein a discrete track method and a magnetic recording
medium produced thereby will be called a discrete track medium.
[0010] An exemplary discrete track medium is a magnetic recording
medium which is formed on a non-magnetic substrate having an uneven
pattern formed thereon and a physically-isolated magnetic recording
track and a servo signal pattern are formed on the medium (see, for
example, Patent Document 1). In the disclosed magnetic recording
medium, a ferromagnetic layer is formed via a soft magnetic layer
on the substrate surface with unevenness. A protective film is
formed on the surface of the ferromagnetic layer. In this magnetic
recording medium, a physically-isolated magnetic recording area is
formed around a raised area.
[0011] According to the disclosed magnetic recording medium,
generation of a magnetic wall on the soft magnetic layer can be
avoided, influence of the heat fluctuation can thus be made small
and no interference occurs between adjacent signals. As a result, a
high-density magnetic recording medium with less noise can be
provided. The discrete track method includes a method of forming a
track after a magnetic recording medium consisting of several
layers of thin films is formed, and a method of forming an uneven
pattern on a substrate surface directly or on a thin film layer for
track formation, and then forming a thin film of a magnetic
recording medium (see, for example, Patent Documents 2 and 3). The
former process is often called a magnetic layer processing. The
latter process is often called an embossing process.
[0012] Patent Document 4 discloses a method of forming an area
between magnetic tracks of a discrete track medium by injecting
nitrogen ions and oxygen ions into a previously formed magnetic
layer or by irradiating with laser. Patent Document 5 discloses
employing carbon as a mask used for an ion milling process of the
magnetic layer. Patent Document 6 discloses forming a ferromagnetic
material layer including one of the elements of Fe, Co and Ni on a
substrate, selectively masking a surface of the ferromagnetic
material layer, exposing an exposed section with reactant gas
including halogen and chemically modifying a magnetic property of
the exposed section and a layer therebelow by chemical reaction to
form a non-ferromagnetic material area.
[0013] A protective layer of hard carbon is formed on a surface of
the magnetic recording medium. The protective layer protects
information recorded on the recording layer from being accidentally
interfered with by the magnetic head. The protective layer
increases slidability of the magnetic head. However, since
durability of the magnetic recording medium is still insufficient
by providing the protective layer, a lubricant is applied to the
surface of the protective layer to the thickness of about 0.5 to10
nm so as to improve durability of the protective layer. Examples of
the lubricant include a perfluoropolyether-based lubricant and an
aliphatic hydrocarbon-based lubricant. The lubricant is made to
adhere to the protective layer so as to mainly prevent the magnetic
head slider from directly interfering with the protective layer and
to significantly reduce frictional force of the magnetic head
slider which slides on the magnetic recording medium.
[0014] Patent Document 1: Japanese Unexamined Patent Application,
First Publication No. 2004-164692
[0015] Patent Document 2: Japanese Unexamined Patent Application,
First Publication No. 2004-178793
[0016] Patent Document 3: Japanese Unexamined Patent Application,
First Publication No. 2004-178794
[0017] Patent Document 4: Japanese Unexamined Patent Application,
First Publication No. 5-205257
[0018] Patent Document 5: Japanese Unexamined Patent Application,
First Publication No. 2006-31849
[0019] Patent Document 6: Japanese Unexamined Patent Application,
First Publication No. 2002-359138
SUMMARY OF THE INVENTION
[0020] Generally, a magnetic recording medium having a discrete
pattern or a bit pattern is produced by forming a magnetic layer of
which the surface has recessed areas and raised areas and then
filling up the recessed areas with a non-magnetic material so as to
smooth the surface. If, however, a magnetic recording medium is
produced by forming a mask layer corresponding to the magnetic
pattern on the surface of the magnetic layer, partially
non-magnetizing the magnetic layer by doping ions or other
substances and forming a magnetic pattern on the magnetic layer,
the surface of the magnetic recording medium is smoothed without
being filled with the non-magnetic material.
[0021] There has been a problem that, if the surface of the
magnetic recording medium is uneven and thus is not smooth, a
lubricant cannot be applied uniformly onto the surface of the
magnetic recording medium. Even if the lubricant layer is once
formed uniformly, the thickness of the lubricant layer may be
reduced over time, which may cause a crash of the magnetic
recording reproducing head within the hard disk drive.
[0022] The invention provides a production method for a magnetic
recording medium with a discrete pattern or a bit pattern, in which
a lubricant layer can be reliably formed even on a surface on which
unevenness still remains and thickness of the lubricant layer is
not reduced over time.
[0023] In view of the production methods for magnetic recording
media disclosed in the foregoing Patent Documents, the present
inventors have developed a method of partially non-magnetizing a
magnetic layer by providing a mask layer corresponding to the
magnetic pattern on the surface of the magnetic layer and causing
the surface of the magnetic layer exposed through the mask layer to
chemically react with oxygen gas or other substance.
[0024] The present inventors have also found that, when the method
is employed, reactivity between the oxygen gas or other substance
and the magnetic layer is increased if a surface of a reaction area
of the magnetic layer is slightly removed.
[0025] The thus-obtained magnetic recording medium has minor
unevenness on a surface thereof. It is preferred to eliminate the
unevenness by filling the recessed areas with a non-magnetic
material. The smoothing process to fill the non-magnetic material,
however, may probably contaminate the surface of the magnetic
recording medium. The manufacturing process may also become
complicated, which may increase the cost of the magnetic recording
medium. Accordingly, the smoothing process is difficult to be
employed. Accordingly, in order to obtain a clean magnetic
recording medium surface, unevenness within tolerance is left on
the surface of the magnetic recording medium.
[0026] If a lubricant layer is formed on an uneven surface of the
magnetic recording medium, the lubricant cannot be applied
uniformly as described above. Even if the lubricant layer is once
formed uniformly, the thickness of the lubricant layer may be
reduced over time, which may cause a crash of the magnetic
recording reproducing head within the hard disk drive.
[0027] In order to solve the aforementioned problems, the present
inventors have intensively studied and finally completed the
invention. The invention relates to the following.
[0028] (1) A production method for a magnetic recording medium
which includes, on at least one surface of a non-magnetic
substrate, a magnetic pattern formed by magnetically isolating a
magnetic layer when seen from a side of a surface of the magnetic
recording medium, the magnetic pattern being formed by the magnetic
layer and an isolated area defined around the magnetic layer, and
the isolated area having a recessed area with respect to the
magnetic pattern, the method including forming a lubricant layer on
a surface of the magnetic recording medium by the steps of
applying, onto the surface of the magnetic recording medium, a
first lubricant with high wettability of the surface of the
magnetic recording medium with respect to the lubricant; and
applying a second lubricant onto the surface of the magnetic
recording medium onto which the first lubricant has been
applied.
[0029] (2) The production method for a magnetic recording medium
according to (1), in which a molecular weight of the first
lubricant is smaller than that of the second lubricant.
[0030] (3) The production method for a magnetic recording medium
according to (1) or (2), in which after the first lubricant is
applied to the surface of the magnetic recording medium, the first
lubricant applied to the surface of the magnetic recording medium
is partially washed out and then the second lubricant is applied to
the surface of the magnetic recording medium.
[0031] (4) The production method for a magnetic recording medium
according to any one of (1) to (3), in which the surface of the
magnetic recording medium is washed with water before the first
lubricant is applied to the surface of the magnetic recording
medium.
[0032] (5) A magnetic recording and reproducing apparatus which
includes in combination: a magnetic recording medium produced by
the production method for a magnetic recording medium according to
any one of (1) to (4); a driving section which drives the magnetic
recording medium toward a recording direction; a magnetic head
which includes a recording section and a reproducing section; a
device for causing the magnetic head to relatively move with
respect to the magnetic recording medium; and a recording and
reproducing signal processing device which inputs signals to the
magnetic head and reproduces output signals from the magnetic
head.
[0033] According to the invention, in the magnetic recording medium
having a discrete pattern or a bit pattern, a lubricant layer can
be provided reliably even if unevenness remains on the surface of
the magnetic recording medium. Thus, a reliable magnetic recording
and reproducing apparatus can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 schematically illustrates a state of a lubricant on a
surface of a magnetic recording medium to which the invention is
applied.
[0035] FIG. 2 schematically illustrates a section structure of a
substrate and a magnetic layer of the magnetic recording medium
according to an embodiment to which the invention is applied.
[0036] FIG. 3 is a flowchart schematically illustrating an
exemplary production method for the magnetic recording medium
according to the invention.
[0037] FIG. 4 illustrates a configuration of a magnetic recording
and reproducing apparatus according to the invention.
[0038] FIG. 5 schematically illustrates a state of a lubricant on a
surface of a related art magnetic recording medium.
DESCRIPTION OF REFERENCE NUMERALS
[0039] 1: non-magnetic substrate
[0040] 2: magnetic layer
[0041] 3: carbon mask layer
[0042] 4: resist layer
[0043] 5: stamp
[0044] 6: ion milling
[0045] 7: removed portion
[0046] 8: resist layer
[0047] 9: protective film layer
[0048] 10: oxygen or ozone
[0049] 11: inactive gas
[0050] 12: lubricant layer
[0051] 12a: first lubricant
[0052] 12b: second lubricant
[0053] 21: magnetic property decreased area
[0054] 22: recessed area
[0055] 23: raised area
[0056] 30: magnetic recording medium
[0057] 31: magnetic head
[0058] 32: recording and reproducing signal system
[0059] 33: head driving section
[0060] 34: medium driving section
[0061] 41: magnetic recording and reproducing device
DETAILED DESCRIPTION OF THE INVENTION
[0062] Hereinafter, a production method for a magnetic recording
medium and a magnetic recording and reproducing apparatus to which
the invention is applied will be described in detail with reference
to the drawings.
[0063] First, a configuration of a lubricant layer 12 formed on a
surface of a magnetic recording medium 30 as illustrated in FIG. 1
will be described as an embodiment of the invention. As illustrated
in FIGS. 1(a) and 1(b), the lubricant layer 12 adheres to a surface
of a protective layer (not shown) formed on the surface of the
magnetic recording medium 30 so as to prevent a magnetic head
slider from directly interfering with the protective layer. The
lubricant layer 12 significantly reduces frictional force of the
magnetic head slider which slides on the magnetic recording medium
30.
[0064] The invention relates to a production method for the
magnetic recording medium 30. The magnetic recording medium 30 has
a magnetic pattern on at least one surface of the non-magnetic
substrate 1 formed by magnetically isolating the magnetic layer 2.
The magnetic pattern includes the magnetic layer 2 and an isolated
area formed around the magnetic layer 2 when seen from the
lubricant layer 12 side. The isolated area forms a recessed area 22
with respect to the magnetic pattern. A lubricant layer 12 is
formed on the surface of the magnetic recording medium 30 by
applying, onto the surface of the magnetic recording medium 30, a
first lubricant 12a for improving wettability of the surface of the
magnetic recording medium 30 with respect to a second lubricant,
and then applying the second lubricant 12b onto the surface of
magnetic recording medium 30 on which the first lubricant 12a has
been applied.
[0065] In a related art production method for a magnetic recording
medium, since a surface of a magnetic recording medium is very
smooth, when a lubricant is applied to the surface of the magnetic
recording medium, the lubricant spreads on the surface uniformly so
as to provide a lubricant layer of uniform thickness over the
entire surface of the magnetic recording medium.
[0066] On the contrary, when unevenness remains on the surface as
in the magnetic recording medium of the invention, a problem may
arise that the lubricant cannot be applied uniformly. In addition,
even if the lubricant is once applied to the entire surface to form
a lubricant layer, the thickness of the lubricant layer will be
reduced over time due to space formed inside the lubricant layer.
Thus, there is a possibility that the magnetic recording
reproducing head may crash within the hard disk drive.
[0067] The present inventors have further examined this phenomenon
and found that, as illustrated in FIG. 5(a), for example, when the
lubricant 112 is applied to the surface of the magnetic recording
medium 130 with unevenness remaining thereon, the lubricant gathers
to an edge portion of the raised area 123 on the surface of the
magnetic recording medium 130. Thus, the lubricant layer 112 cannot
be uniformly formed on the surface of the magnetic recording medium
130. It has been also found that, as illustrated in FIG. 5(b), for
example, since the gathered lubricant moves toward an upper surface
of a recessed area 122 or a raised area 123 over time, the
thickness of the lubricant layer 112 at the raised areaside surface
of the magnetic recording medium may be reduced. As a result,
protection performance of the lubricant layer 112 may be impaired
and the magnetic recording reproducing head may crash.
[0068] In order to solve these problems, in the invention, a
lubricant layer is formed uniformly on the entire magnetic
recording medium by applying a first lubricant having high
wettability with respect to the surface of the magnetic recording
medium onto the surface of the magnetic recording medium, and then
a step of applying a second lubricant onto the surface of the
magnetic recording medium on which the first lubricant has been
applied. Here, the term "first lubricant with high wettability"
means the first lubricant having higher wettability than that of
the second lubricant. After the first lubricant is applied
uniformly on the surface of the magnetic recording medium, the
second lubricant can be uniformly applied to the surface of the
magnetic recording medium. For example, as illustrated in FIG.
1(a), after the first lubricant 12a is applied to the surface of
the magnetic recording medium 30 and the wettability with respect
to the second lubricant of the surface of the magnetic recording
medium 30 is increased, the second lubricant 12b is applied to the
surface of the magnetic recording medium 30. In this manner, the
lubricant layer 12 is uniformly formed over the entire surface of
the magnetic recording medium.
[0069] The lubricant layer 12 used in the invention is not
particularly limited so long as it is chemically stable, low in
frictional coefficient and in adsorption. Examples thereof may
include a fluoro-resin-based lubricant. Examples of widely used
fluoro-resin-based lubricant include perfluoropolyether. Examples
of perfluoropolyether include Fomblin Z-DOL and Fomblin Z-TETRAOL
(trade names) available from Solvay Solexis.
[0070] These substances may be used alone or in combination. For
example, a cyclotriphosphazene-based lubricant and a
perfluoropolyether-based lubricant may be used in combination, and
a perfluoropolyether compound having a phosphazene ring at a
terminal group and a perfluoropolyether compound having a hydroxyl
group at a terminal group may be used in combination as a
lubricant.
[0071] The above-described fluoro-resin-based lubricant is often
dissolved or dispersed in a fluorine-based solvent and is applied
to a protective film formed on the surface of the magnetic
recording medium 30. Examples of the method of applying the
fluoro-resin-based lubricant may include spin-coating the solution
including the lubricant onto the surface of the magnetic recording
medium 30. Alternatively, a solution is placed in a lubricant
storage tank in which a magnetic recording medium 30 is immersed,
then the magnetic recording medium 30 is taken out of the lubricant
storage tank at a predetermined speed so as to form a lubricant
film of uniform thickness on the surface of the magnetic recording
medium 30 (dipping). Examples of the fluorine-based solvent used
for dissolution of the fluoro-resin-based lubricant may include
Vertrel XF (trade name) available from DuPont-Mitsui
Fluorochemicals.
[0072] The first lubricant 12a and the second lubricant 12b which
constitute the lubricant layer 12 of the invention may be the same
or different compounds. If different compounds are employed, the
first lubricant 12a and the second lubricant 12b may have the same
molecular weight.
[0073] If the first lubricant 12a and the second lubricant 12b
which constitute the lubricant layer 12 are different compounds and
used in the same molecular weight, the average molecular weight is
preferably in the range of 500 to 5000 and more preferably in the
range of 500 to 3000. The average molecular weight of less than 500
is not preferred since the lubricant is easily vaporized while the
hard disk drive is in operation and lubricating performance becomes
insufficient. The average molecular weight exceeding 5000 is also
not preferred since viscosity unfavorably increases and mobility
and applicability deteriorate. The average molecular weight in the
range described above preferably provides excellent mobility,
applicability and temporal stability.
[0074] Since the first lubricant 12a and second lubricant 12b of
the lubricant layer 12 are fundamentally similar in type, it is
considered that both the lubricants diffuse into each other after
applying the second lubricant 12b. Accordingly, as shown in the
schematic diagram illustrated in FIGS. 1(a) and 1(b), it is
considered that the boundary of the first lubricant 12a and the
second lubricant 12b is not defined clearly. However, it is
considered that the outermost surface of the lubricant layer 12 is
covered with the second lubricant 12b.
[0075] In the invention, it is preferred that organic compounds of
the same structure with varying degree of polymerization are used
as the first lubricant 12a and the second lubricant 12b. It is also
preferred that the molecular weight of the first lubricant 12a is
smaller than that of the second lubricant 12b.
[0076] It is generally known that a lubricant with increased
molecular weight has a higher boiling point and increased high
temperature stability. Accordingly, since the temperature inside
the hard disk drive often reaches as high as 80.degree. C.
depending on the usage environment, a lubricant with high molecular
weight is often used. Since a lubricant with high molecular weight
has high viscosity, however, if the lubricant is applied to an
uneven surface of the magnetic recording medium, the lubricant
especially gathers easily on the surface.
[0077] Accordingly, in the invention, coverage of the lubricant on
the surface of the magnetic recording medium 30 with unevenness
remaining thereon is increased by using a lubricant with low
molecular weight as the first lubricant 12a. At the same time,
wettability thereof with respect to the second lubricant is
increased. It is preferred to then apply the second lubricant 12b
to the surface of the magnetic recording medium 30 on which the
first lubricant 12a has been applied, in order to form a lubricant
layer 12 over the entire surface of the magnetic recording medium
30.
[0078] Here, the first lubricant 12a has an average molecular
weight of preferably in the range of 500 to 2500 and more
preferably in the range of 500 to 2000. The second lubricant 12b
has an average molecular weight of preferably higher than that of
the first lubricant 12a, which is preferably in the range of 1000
to 4000 and more preferably in the range of 1500 to 3000.
[0079] In the invention, after the first lubricant 12a is applied
to the surface of the magnetic recording medium 30, the magnetic
recording medium 30 is immersed in a solvent so as to partially
wash the first lubricant 12a adhering to the surface of the
magnetic recording medium 30. Then, the second lubricant 12b is
preferably applied to the surface of the magnetic recording medium
30. As described above, although a lubricant with low molecular
weight has low viscosity and thus applicability to the surface of
the magnetic recording medium with unevenness is high, since a
boiling point thereof is low, protection of the surface of the
magnetic recording medium is not high. Accordingly, as illustrated
in FIG. 1(b), after the wettability of the surface of the magnetic
recording medium 30 with respect to the second lubricant is
increased by applying, to the surface of the magnetic recording
medium 30, the first lubricant 12a having smaller molecular weight
than that of the second lubricant 12b, the magnetic recording
medium 30 is immersed in a solvent to wash excess substances of the
first lubricant 12a adhering to the surface of the magnetic
recording medium 30. Then, the second lubricant 12b is applied to
the magnetic recording medium 30. In this manner, the lubricant
layer 12 having high molecular weight and high boiling point can be
applied uniformly. In the invention, it is preferred to employ a
fluorine-based solvent as a solvent that can be used for washout of
the first lubricant. Preferred examples of the fluorine-based
solvent include Vertrel XF (trade name) available from
DuPont-Mitsui Fluorochemicals.
[0080] It is also preferred in the invention that, before applying
the first lubricant 12a to the surface of the magnetic recording
medium 30, the surface of the magnetic recording medium 30 is
washed with water. Washing the surface of the magnetic recording
medium 30 with water has the following effects: dust adhering to
the surface of the magnetic recording medium 30 can be removed;
wettability of the surface of the magnetic recording medium 30 with
respect to the lubricant is increased; and the lubricant layer 12
is uniformly formed on the surface of the magnetic recording medium
30.
[0081] Next, the magnetic recording medium applied to the present
embodiment is described in detail with reference to FIG. 2. In the
present embodiment, although the production method for a magnetic
recording medium of a discrete pattern is used, a similar
production method for a magnetic recording medium of bit pattern
can also be used.
[0082] As illustrated in FIG. 2, the magnetic recording medium 30
applied to the present embodiment is formed by laminating, on a
surface of non-magnetic substrate 1, a soft magnetic layer, an
intermediate layer, a magnetic layer 2 and a protective film layer.
The magnetic layer 2 includes a magnetic area and an isolated area
in which the magnetic pattern is formed.
[0083] A lubricating film is formed on an outermost surface of the
magnetic recording medium 30. A magnetic area which is a magnetic
pattern area is isolated by the isolated area. Only the substrate 1
and the magnetic layer 2 are illustrated in FIG. 2.
[0084] On the magnetic layer 2, the surface sections at certain
areas are removed to provide recessed areas 22. Here, d represents
the depth of the recessed area 22. The bottom of the recessed area
22 is formed as an area 21 at which a magnetic property has been
decreased through, for example, non-magnetization (hereinafter,
referred to as a "magnetic property decreased area").
[0085] As illustrated in FIG. 2, the magnetic layer 2 is isolated
by the magnetic property decreased area 21 and the recessed area 22
to provide a raised area 23 serving as a magnetic area. In the
present embodiment, the magnetic property decreased area 21 is also
included in the non-magnetized area.
[0086] Next, the production method for of the magnetic recording
medium 30 of the present embodiment will be described in detail
with reference to FIG. 3.
[0087] As illustrated in FIG. 3, the production method for the
magnetic recording medium 30 includes, in this order: a step A of
forming at least the magnetic layer 2 on the non-magnetic substrate
1; a step B of forming the carbon mask layer 3 on the magnetic
layer 2; a step C of forming a resist layer 4 on the carbon mask
layer 3; a step D of forming a negative pattern of a magnetic
pattern on the resist layer 4 by transferring using a stamp 5 (the
term "negative pattenr" herein is a pattern which has recessed
areas formed in the resist layer corresponding to the recording
track in order to isolate the recording track) (an arrow in the
step D represents a motion of the stamp 5 and the reference numeral
8 represents a resist layer remaining after the formation of the
negative pattern); a step E of removing a portion corresponding to
the negative pattern of the magnetic pattern from the resist layer
8 and the carbon mask layer 3 remaining even after the transfer; a
step F of removing, by ion milling 6, an exposed surface section of
the magnetic layer 2 remaining after the removal of the carbon mask
3 (reference numeral 7 represents the removed portion); and a step
G which includes forming a non-magnetized area on the magnetic
layer 2 from which the surface section has been removed, exposing
the formed area to, for example, oxygen and ozone 10 or irradiating
the formed area with laser, and subsequently removing the resist 4
and the carbon mask layer 3.
[0088] In addition to the above-described steps, it is preferred to
expose a surface to fluorine-based gas before the step of forming
the non-magnetized area at the portion corresponding to the
negative pattern of the magnetic pattern of the magnetic layer 2.
It is also preferred to provide a step H of irradiating inactive
gas 11, such as Ar, to slightly remove the surface section of the
magnetic layer 2 and a step I of forming a protective film layer 9
on the removed area after the resist layer 4 and the carbon mask
layer 3 are removed.
[0089] The non-magnetic substrate 1 may be any substrate so long as
it is a non-magnetic substrate. Examples thereof include an Al
alloy substrate, such as Al--Mg alloy, having Al as a principle
component, and substrates of normal soda glass,
aluminosilicate-based glass, crystallized glass silicon, titanium,
ceramic and various resins. Among these, glass substrates, such as
an Al alloy substrate and crystallized glass, or silicon substrates
are preferably used. Average surface roughness (Ra) of these
substrates is not more than 1 nm, preferably not more than 0.5 nm
and more preferably not more than 0.1 nm.
[0090] An in-plane magnetic layer or a perpendicular magnetic layer
can be used as the magnetic layer 2. The perpendicular magnetic
layer is especially preferable from the viewpoint of high recording
density. The magnetic layer 2 is preferably produced by a Co-based
alloy.
[0091] Here, as a magnetic layer for an in-plane magnetic recording
medium, for example, a lamination structure consisting of a
non-magnetic CrMo underlayer and a ferromagnetic CoCrPtTa magnetic
layer can be used.
[0092] As a magnetic layer for a perpendicular magnetic recording
medium, for example, a lamination structure consisting of a backing
layer of, for example, an FeCo alloy (e.g., FeCoB, FeCoSiB, FeCoZr,
FeCoZrB and FeCoZrBCu) having a soft magnetic property, a FeTa
alloy (e.g., FeTaN and FeTaC) and a Co alloy (e.g., CoTaZr, CoZrNB
and CoB), an orientation controlling film, such as Pt, Pd, NiCr and
NiFeCr, an intermediate layers, which will be provided as
necessary, and a magnetic layer having a granular structure
consisting of a 67Co-18Cr-15Pt alloy or a 70Co-5Cr-15Pt-10SiO.sub.2
alloy may be used.
[0093] In the present embodiment, a magnetic layer having a
granular structure is preferably employed as the magnetic layer 2
from the viewpoint of increasing reactivity at the time of forming
a non-magnetized area. The magnetic layer having the granular
structure herein is a magnetic layer in which an oxide covers the
circumference of the magnetic particle.
[0094] Examples of the oxide include a Ti oxide, a W oxide, a Cr
oxide, a Co oxide, a Ta oxide and a Ru oxide other than the
above-described SiO.sub.2.
[0095] The thickness of the magnetic layer 2 is not less than 3 nm
and not more than 20 nm and preferably not less than 5 nm and not
more than 15 nm. It suffices that the magnetic layer 2 is formed to
provide sufficient input and output performance of the head in
accordance with the type and the lamination structure of the
magnetic alloy used. The thickness of the magnetic layer 2 is
defined to obtain predetermined output greater than certain output
at the time of reproduction. Usually, since parameters representing
the recording reproduction characteristic are reduced as the output
increases, it is therefore necessary to determine the optimum
thickness. The magnetic layer 2 is formed as a thin film by
sputtering.
[0096] In the present embodiment, the carbon mask layer 3 which
includes a carbon film is formed on the surface of the magnetic
layer 2. Since the carbon film which constitutes the carbon mask
layer 3 is easy in dry etching (i.e., reactive ion etching or
reactant ion milling) using oxygen gas, residue can be reduced and
contamination on the surface of the magnetic recording medium 30
can be decreased in the step G in FIG. 3.
[0097] The carbon film can be formed by sputtering or by a CVD
process. The CVD process can form a carbon film with a higher
compactness. The thickness of the carbon mask layer 3 is preferably
in the range of 5 nm to 40 nm and more preferably in the range of
10 nm to 30 nm. If the thickness of the carbon mask layer 3 is
smaller than 5 nm, the edge portion of the carbon mask layer 3 may
be rolled off, which may impair the formation characteristic of the
magnetic pattern. It is not preferred that the ion that transmitted
the resist layer 4 and the carbon mask layer 3 enters the magnetic
layer 2 and impairs the magnetic property of the magnetic layer 2.
If the thickness of the carbon mask layer 3 is thicker than 40 nm,
longer etching time of the carbon mask layer 3 is necessary and
productivity thus decreases. Further, residue during etching of the
carbon mask layer 3 may unfavorably remain on the surface of the
magnetic layer 2.
[0098] Next, a resist layer 4 is formed on the carbon mask layer 3.
A negative pattern of the magnetic pattern is formed on the resist
layer 4. Although the negative pattern can be formed on the resist
layer by a normal photolithography method, it is preferred to use a
stamp on the resist layer 4 to transfer a negative pattern of the
magnetic pattern from the viewpoint of operation efficiency.
[0099] In the present embodiment, as illustrated in the step D in
FIG. 3, it is preferred to define the thickness of the resist layer
8 remaining in the recessed area of the resist layer 4 after the
negative pattern of the magnetic pattern is formed on the resist
layer 4 in the range of 0 to 20 nm. When the thickness of the
remained layer in the resist layer 4 is in contrtolled in this
range, edge roll-off of the mask layer 3 during an etching process
of the carbon mask layer 3 and the magnetic layer 2 can be avoided
as illustrated in the step E in FIG. 3. At the same time, the
shield ability with respect to the milling ion of the carbon mask
layer 3 and the magnetic pattern formation characteristic by the
carbon mask layer 3 can be improved.
[0100] In the present embodiment, it is preferred to employ a
radiation-curable material for the resist layer 4 illustrated in
the step C in FIG. 3. It is also preferred to irradiate the resist
layer 4 with radiation during or after transferring a pattern onto
the resist layer 4 using the stamp 5. Thus, the configuration of
the stamp 5 can be transferred highly precisely onto the resist
layer 4. In the etching process of the carbon mask layer 3 as
illustrated in the step E in FIG. 3, edge roll-off of the carbon
mask layer 3 can be avoided, and shield ability of the carbon mask
layer 3 with respect to the milling ion can be improved and the
magnetic pattern formation characteristic by the carbon mask layer
3 can be improved.
[0101] Examples of the radiation used in the present embodiment
include a wide range of electromagnetic waves, such as heat ray,
visible light, ultraviolet ray, X-ray and gamma ray. Examples of
the radiation-curable material include heat-curing resin in case of
the heat ray and ultraviolet curing resin in case of the
ultraviolet ray.
[0102] In the present embodiment, in the step of transferreing a
pattern onto the resist layer 4 using the stamp 5, the stamp 5 is
pressed against the resist layer 4 in a state in which the mobility
of the resist layer 4 is high. With the stamp 5 being pressed, the
resist layer 4 is cured when irradiated with radiation. The stamp 5
is then removed from the resist layer 4. In this manner, the
configuration of the stamp 5 can be transferred highly precisely to
the resist layer 4.
[0103] Several methods are proposed to irradiate the reisist layer
4 with radiation while the stamp 5 is pressed against the resist
layer 4. For example, the resist layer 4 may be irradiated at an
opposite side of the stamp 5, i.e., a side of the substrate. The
resist layer 4 may be irradiated at the side of the stamp 5 in a
case in which the stamp 5 is made by a radiation-transmittive
material. The resist layer 4 may be irradiated from a side surface
of the stamp 5. The resist layer 4 may be irradiated by heat
conduction of the stamp material or the substrate 1 using highly
conductive radiation with respect to a solid material, such as heat
ray. It is preferred to employ ultraviolet curing resin, such as
novolak-based resin, acrylic ester resin and alicyclic epoxy resin,
as a material of the resist layer 4. It is preferred to employ
glass or resin which is highly transmittive to the ultraviolet ray
as a material of the stamp 5.
[0104] The resist layer 4 is preferably made of SiO.sub.2-based
resist. The SiO.sub.2-based resist is highly resistive to dry
etching using oxygen gas. Thus, in a process of forming a negative
pattern of a magnetic pattern using ion milling on the carbon mask
layer 3, image blurring can be reduced. That is, since the carbon
mask layer 3 can be easily worked by dry etching using oxygen gas
while the SiO.sub.2-based resist is highly resistive to dry etching
using oxygen gas, it becomes possible to work the carbon mask layer
3 into a configuration to stand upright by dry etching which can
provide a highly sharp magnetic pattern.
[0105] If the carbon mask layer 3 is removed and the resist remains
in the recessed area after the formation of the negative pattern
(the resist is denoted by a reference numeral 8 in the step D in
FIG. 3), the resist 8 is removed (see the step E in FIG. 3). Dry
etching, such as reactive ion etching and ion milling, is used for
the removal of the carbon mask and the resist.
[0106] In the present embodiment, the area on the magnetic layer 2
that is not covered with the carbon mask layer 3 and the resist
layer 4 is non-magnetized in the foregoing method. Before the
non-magnetization, the magnetic layer 2 at that area is removed.
The surface section (d illustrated in the step F in FIG. 3) of the
magnetic layer 2 is preferably removed to a thickness range of 0.1
nm to 15 nm. The surface section of the magnetic layer 2 may
deteriorate under the influence of the carbon mask layer 3
laminated thereon or the influence of the atmosphere. If the
surface section deteriorates, the non-magnetizing reaction of the
magnetic layer 2 may not work effectively.
[0107] The magnetic layer 2 is removed by dry etching the magnetic
layer 2 in the ion milling succeedingly after the dry etching the
carbon mask layer 3, for example by ion milling or reactive ion
etching. In this manner, the edge portion of the remaining magnetic
layer 2 can stand upright. This is because the carbon mask layer 3
is formed upright on the magnetic layer 2 and the magnetic layer 2
formed therebelow also has the similar configuration. In this
manner, the magnetic layer 2 with excellent fringe performance can
be provided.
[0108] As described above, it is preferred to perform reactive ion
etching of the carbon mask layer 3 using oxygen gas in the present
embodiment. It is also preferred to perform ion milling of the
magnetic layer 2 using inactive gas, such as argon and nitrogen.
That is, the milling ion for the carbon mask layer 3 and the
milling ion for the magnetic layer 2 are preferably replaced with
optimal milling ion.
[0109] It is preferred to expose an area on the magnetic layer 2
which is not covered with the carbon mask layer 3 and the resist
layer 4 with fluorine-based gas before that area is subject to
non-magnitization. In this manner, the reactivity of surface of the
magnetic layer 2 is improved and the non-magnetizing reaction can
be performed more efficiently.
[0110] In the present embodiment, it is preferred to employ a
magnetic layer having a granular structure as the magnetic layer 2
as described above. The magnetic layer having a granular structure
is a magnetic layer in which an oxide covers the circumference of a
magnetic particle. Since the magnetic crystal is isolated by a
non-magnetic phase, magnetic interaction between magnetic grains is
weak. Since the magnetic crystal grain is fine, the magnetic layer
of significantly low noise can be formed. If such a magnetic layer
2 is non-magnetized by using oxygen or ozone, an oxide layer
existing in the grain boundary can be selectively etched by a
process in a reactive ion etching device using, for example,
fluorine-based gas. At the same time, oxidation reaction with
metal, such as Co in the magnetic layer 2, and oxygen and ozone can
be promoted, and thus the magnetic property of the magnetic layer 2
can be changed more efficiently.
[0111] In the present embodiment, the magentive layer 2 may have a
two-layer structure of the granular structure and a non-granular
structure formed thereon.
[0112] In the magnetic recording medium 30 of the present
embodiment, as illustrated in FIG. 2, it is preferred that a width
W of the magnetic section of the magnetic layer 2 is not greater
than 200 nm and a width L of the non-magnetic part is not greater
than 100 nm from the viewpoint of increase in recording density.
Accordingly, the track pitch P (i.e., W+L) should be as small as
possible and not greater than 300 nm in order to increase the
recording density in the data area.
[0113] Here, in the magnetically-isolated magnetic pattern of the
invention, it suffices that the magnetic layer 2 is isolated when
seen from a surface side of the magnetic recording medium 30 even
if it is not isolated at the bottom of the magnetic layer 2 in
order to achieve the object of the invention. Such a
magnetically-isolated magnetic pattern is also included in the
scope of the magnetically-isolated magnetic pattern of the the
invention. The magnetic pattern of the invention may include a bit
pattern, a discrete pattern, a servo data signal pattern and a
burst signal pattern. In the bit pattern, the magnetic pattern is
disposed regularity for every 1 bit. In the discrete pattern, the
magnetic pattern is disposed on a track pattern.
[0114] It is preferred to apply the present embodiment to a
discrete pattern magnetic recording medium from the viewpont of
simplicity in manufacture. In the discrete pattern magnetic
recording medium, magnetically-isolated magnetic patterns are the
magnetic recording track and servo signal patterns.
[0115] In the production of the magnetic recording medium 30 of the
present embodiment, the resist layer 4 and the carbon mask layer 3
formed on the magnetic layer 2 are removed after the magnetic layer
2 is partially non-magnetized. It is preferred to remove the resist
layer and the mask layer by dry etching, reactive ion etching or
ion milling.
[0116] In production of the recording medium 30 of the present
embodiment, the surface section is preferably etched using inactive
gas, such as Ar, as illustrated in the step H in FIG. 3 to the
thickness range of 1 nm to 2 nm in order to remove the outermost
surface layer that is non-magnetized by ozone or other substances
on the surface of the magnetic layer 2. This is because the surface
of the magnetic layer 2 may become rough in this area.
[0117] In the present embodiment, as illustrated in the step I in
FIG. 3, the protective film layer 9 is formed on the surface of the
magnetic layer 2 after the resist layer 4 and the carbon mask layer
3 are removed (i.e., in a magnetic area (raised area 23), an area
in which a non-magnetic material is buried ("magnetic property
decreased area 21") or an area of the recessed area 22 in which no
non-magnetic material is buried as illustrated in FIG. 2).
[0118] The protective film layer 9 may be a carbonaceous layer
consisting of carbon (C), hydrogenated carbon (HxC), carbon nitride
(CN), amorphous carbon and silicon carbide (SiC), or other usually
employed protective film layer material, such as SiO.sub.2,
Zr.sub.2O.sub.3 and TiN. The protective film layer 9 may include
two or more layers.
[0119] The thickness of the protective film layer 9 needs to be not
greater than 10 nm. The thickness of the protective film layer 9
greater than 10 nm is not preferred since the head and the magnetic
layer are away from each other, which may cause the input and
output signal intensity to become insufficient. The protective film
layer 9 can be formed by sputtering or a CVD process.
[0120] The lubricant layer 12 is formed on the protective film
layer 9 as described above (see FIGS. 1(a) and 1(b)). The lubricant
layer 12 is usually formed to the thickness of 1 to 4 nm.
[0121] Next, a configuration of the magnetic recording and
reproducing apparatus 41 to which the invention is applied is
illustrated in FIG. 4. The magnetic recording and reproducing
apparatus 41 according to the invention includes the magnetic
recording medium 30, a medium driving section 34, a magnetic head
31, a head driving section 33 and a recording and reproducing
signal system 32. The medium driving section 34 drives the magnetic
recording medium 30 to a recording direction. The magnetic head 31
includes a recording section and a reproducing section. The head
driving section 33 causes the magnetic head 31 to be relatively
moved with respect to the magnetic recording medium 30. The
recording and reproducing signal system 32 has a combined function
of signal input to the magnetic head 31 and a recording and
reproducing signal processing device for reproducing output signals
from the magnetic head 31. A combination of these components can
provide a magnetic recording and reproducing apparatus 41 with high
recording density. In the related art, the width of the reproducing
head has been narrower than that of the recording head in order to
eliminate influence of magnetizing transition areas at track edge
portions. In the invention, however, the reproducing head width and
the recording head width are substantially the same because the
magnetic track of the the magnetic recording medium 30 has a
magnetically-discontinuous configuration. Accordingly sufficient
reproduction output and high SNR can be obtained.
[0122] Further, when the reproducing section of the magnetic head
31 is made of a GMR head or a TMR head, sufficient signal strength
can be obtained even under high recording density. Thus, a magnetic
recording and reproducing apparatus 41 with high recording density
can be provided. If the raising amount of the magnetic head 31 is
controlled to 0.005 .mu.m to 0.020 .mu.m, which is lower than that
of the related art, both the output and the device SNR are
incrased. As a result, a high-capacity and highly-reliable magnetic
recording and reproducing apparatus 41 can be provided. If a signal
processing circuit of a maximum likelihood decoding system is
introduced, the recording density can further be improved. A
sufficiently high SNR can be provided even if the recording and
reproducing are performed with the track density of not less than
100K tracks per inch, linear recording density of 1000 KB per inch
and the recording density of not less than 100 GB per 1 square
inch.
Examples
[0123] Hereinafter, Examples and Comparative Examples will be
described to further illustrate the effect of the invention.
However, the invnention is not limited to these Examples.
(Production of Magnetic Recording Medium)
[0124] A vacuum chamber with a glass substrate for the HD being
placed therein was evacuated to less than 1.0.times.10.sup.-5 Pa in
advance. The glass substrate used herein was crystallized glass
constituted by Li.sub.2Si.sub.2O.sub.5, Al.sub.2O.sub.3--K.sub.2O,
Al.sub.2O.sub.3--K.sub.2O, MgO--P.sub.2O.sub.5 and
Sb.sub.2O.sub.3--ZnO. The glass substrate was dimensioned such that
an outer diameter was 65 mm, an innter diameter was 20 mm and an
average surface roughness (Ra) was 2 .ANG..
[0125] On the glass substrate, thin layers are laminataed by DC
sputtering in the following order: a .sub.60Fe.sub.30Co.sub.10B
soft magnetic layer; a Ru intermediate layer; a
70Co-5Cr-15Pt-10SiO.sub.2 alloy magnetic layer having a granular
structure. A carbon mask layer was laminated thereon by a P-CVD
process. The thickness of the 60Fe30Co10B soft magnetic layer was
60 nm, the thickness of the Ru intermediate layer was 10 rim, the
thickness of the magnetic layer was 15 nm and the thickness of the
carbon mask layer was 30 nm. A SiO.sub.2 resist was spin-coated on
the uppermost layer to the thickness of 100 nm.
[0126] A stamp was pressed against the resist layer at the pressure
of 1 MPa (about 8.8 kgf/cm.sup.2) using a glass stamp having a
negative pattern of the magnetic pattern. Then, the stamp was
removed from the resist layer and the magnetic pattern was
transferred to the resist layer. The magnetic pattern transferred
to the resist layer had a 120 nm-wide circular shape at a raised
area of the resist at the data area and had a 120 nm-wide circular
shape at a recessed area of the resist. The thickness of the resist
layer was 80 nm and the thickness of the recessed area (i.e.,
bottom) of the resist layer was about 5 nm. The resist layer
recessed area was angled about 90 degrees with respect to the
substrate surface.
[0127] First, the resist layer remaining in the recessed area was
removed using CF.sub.4 at 0.5 Pa and 40 seem with the plasma power
of 200 W, the bias of 20 W and the etching time of 10 seconds.
[0128] Then, the carbon mask layer on the recessed area of the
resist layer was removed by dry etching and the surface section of
the magnetic layer was removed by ion etching. The conditions for
dry etching on the carbon mask layer were using O.sub.2 gas of 40
seem, pressure of 0.3 Pa, high-frequency plasma power of 300 W, DC
bias of 30 W and etching time of 30 seconds.
[0129] The magnetic layer was produced using N.sub.2 gas of 10
seem, pressure of 0.1 Pa, accelerating voltage of 300V and etching
time of 5 seconds. The depth (d illustrated in the step F in FIG.
3) of the recessed area of the magnetic layer was about 1 nm. Then,
areas not covered with the carbon mask layer on the magnetic layer
were exposed to gaseous ozone. The magnetic layer was exposed to
the gaseous ozone that flows at 40 sccm in the chamber under the
conditions of 1 Pa and 10 seconds with the substrate temperature of
150.degree. C.
[0130] The carbon mask layer and the resist layer on the surface of
the magnetic recording medium were then removed by dry etching.
Then, in an ion milling device, the surface of the magnetic layer
was etched to the thickness range of about 1 nm to 2 nm using Ar
gas of 10 seem, 0.5 Pa and 5 seconds. A carbon protective film was
formed to the thickness of 5 nm by a CVD process.
Example 1
[0131] A lubricant of perfluoropolyether (Tetraol (trade name))
having an average molecular weight of 1500 was applied to the
thus-produced magnetic recording medium as a first lubricant to the
thickness of I nm. Vertrel (trade name) was used as the
solvent.
[0132] Concentration of the solution was 0.3 mass %. After the
lubricant was applied, the magnetic recording medium was left for
about 30 minutes. Then, a lubricant consisting of
perfluoropolyether having an average molecular weight of 2200 was
applied as a second lubricant to the thickness of 1 nm.
Example 2
[0133] Although the first and the second lubricants were applied in
the same manner as in Example 1, the surface of the magnetic
recording medium was spin-washed with pure water before the first
application of the lubricant. The spin washing was perfouned while
supplying pure water to both sides of the magnetic recording medium
at 5cc/second while the magnetic recording medium was rotated at
200 rpm.
Example 3
[0134] Although the first and the second lubricant were applied in
the same manner as in Example 1, a lubricant consisting of
perfluoropolyether having an average molecular weight of 1000 was
used as the first lubricant.
Example 4
[0135] Although the first and the second lubricants were applied in
the same manner as in Example 3, the magnetic recording medium was
immersed in a solvent (Vertrel (trade name)) for 30 seconds between
application of the first lubricant and application of the second
lubricant. Thickness of the second lubricant was 1.5 nm. Thickness
of the first lubricant after the magnetic recording medium was
immersed in the solvent was 0.5 nm.
Comparative Example
[0136] A lubricant of perfluoropolyether was applied to the
magnetic recording medium to the thickness of 2 nm. Tetraol (trade
name) consisting of perfluoropolyether and having an average
molecular weight of 2200 was used as the lubricant.
(Evaluation of Applicability of Lubricant to Magnetic Recording
Medium)
[0137] In order to evaluate applicability of the lubricant to the
magnetic recording medium, head contamination of the magnetic
recording reproducing head when traveling in a raised manner on the
magnetic recording medium prepared by Examples 1 to 4 and
Comparative Example was evaluated. If the applicability of the
lubricant to the surface of magnetic recording medium was poor, the
lubricant adhered to the head which may easily contaminate the
head.
[0138] The evaluation on the head contamination was performed by
confirming a degree of head contamination when a magnetic certify
test was conducted for 25 sheets (i.e., 50 surfaces) of the
magnetic recording media under predetermined test conditions using
a test head (Tiger3 (trade name) available from TDK/SAE). The
evaluation result is shown in Table 1.
TABLE-US-00001 TABLE 1 Head Contamination Example 1 3% Exmaple 2 1%
Example 3 2% Example 4 0% Comparatice Example 50%
(Evaluation Result)
[0139] As shown in Table 1, the degrees of head contamination of
Examples 1 to 4 were almost less than 3% while the degree of head
contamination of Comparative Example was 50%. From the result, it
was confirmed that the head contamination caused by adhesion of the
lubricant was controlled in Examples 1 to 4 to which the invention
was applied.
INDUSTRIAL APPLICABILITY
[0140] The invention is highly industrially applicable in that,
since a lubricant can be uniformly applied to a surface having an
uneven magnetic pattern formed thereon of a magnetic recording
medium, there is little contamination or breakage of a magnetic
recording reproducing head, and thus a reliable magnetic recording
and reproducing apparatus can be provided.
[0141] It is apparent that the present invention is not limited to
the above Examples but may be modified and changed without
departing from the scope and spirit of the invention.
* * * * *